The present invention relates to methods and apparatus for refrigerating fluids and more particularly, to methods and apparatus for efficiently utilizing the refrigeration available in a liquefied gas.
The refrigeration available from liquefied gases such as liquid nitrogen, liquid argon, etc. is commonly utilized due to the relatively low or cryogenic temperatures at which such liquefied gases are normally produced. For example, it is known to utilize such refrigeration in the condensation of of vapors recovered from a particular process as is illustrated in U.S. Pat. Nos. 4,133,663 and 4,150,494 the latter being assignedto the assignee of the present invention. Typically, the liquefied gas is passed through a multipass indirect heat exchange device in counterflow to the vapors being condensed thereby yielding its refrigeration to and condensing such vapors. It is recognized, however, that due to the intense cold available from such liquefied gases (which typically exist at about -280.degree. F. to -320.degree. F.), steps must be taken to assure that undesirable freezing of fluids which are to be refrigerated is avoided. One such technique for reducing the adverse effects of the intense cold available from liquefied gases is illustrated in U.S. Pat. No. 4,188,793 wherein liquid nitrogen is sprayed (FIG. 4) into a chamber to vaporize the same and form a cold gas which is then utilized to condense a particular volatile vapor. Such condensation results in a warming of the cold gas which is returned by a fan or blower into direct contact with the spray of liquid nitrogen thereby facilitating further vaporization thereof. The rate at which liquid nitrogen is sprayed into contact with the returned gas is controlled by sensing the temperature of such gas and in this manner, the intense refrigeration available from liquid nitrogen may be limited to avoid freezing of condensed vapors. It is noted, however, that blowers which consume shaft power and hence introduce heat into the refrigeration system are required to circulate gas throughout the system thereby reducing the efficiency of refrigerant nitrogen and increasing operating costs. Furthermore, although the temperature of the cold gas utilized to condense vapors is sensed, there are no apparent means utilized to limit heat exchange between such cold gas and the fluid to be condensed and consequently, moisture which may be carried by such fluid may be frozen upon initial heat exchange with the cold gas.
A further technique for utilizing the refrigeration available from a liquefied gas to refrigerate a fluid such as by condensing a vapor is illustrated in U.S. Pat. No. 4,122,684. In the apparatus illustrated in this reference, an intermediate refrigerant such as methane is utilized as a heat transfer medium between the liquefied gas and the particular fluid to be refrigerated. Although freezing of such fluid may be avoided, the use of a separate, intermediate refrigerant requires rather complex apparatus in addition to the cost of providing a separate refrigerant itself and thus renders the overall economics of such vapor condensation questionable.
Accordingly, the prior art evidences a clear need for methods and apparatus for utilizing the refrigeration available in liquefied gas to refrigerate fluids without freezing the same or components thereof while efficiently utilizing the refrigeration available from such liquefied gases.